Glycated Hemoglobin: what is it for and what is the reference value?

Blood tests are very common routines for most people. And, many times, the request for Glycated Hemoglobin appears.

Whether for someone who is just having a check up, to confirm the diagnosis of diabetes or to keep up with the treatment, the exam is very important!

Understand more about glycated hemoglobin and what the results indicate


What is glycated hemoglobin?

Glycated hemoglobin is the binding of glucose (blood sugar) with hemoglobin (protein present in red blood cells).

So, the more sugar (glucose) in the blood, the more connections are made, thereby increasing the rate of glycated hemoglobin in the body. Therefore, the exam is indicated both for the diagnosis and for the follow-up of diabetes.

It is important to note that the test is different from other tests, such as fasting blood glucose. This is because it is able to evaluate the glycemic average of the last 3 or 4 months, approximately.

It is always important that the results are evaluated by professionals, so that individual and clinical factors are considered.

Glycated hemoglobin and blood glucose

Hemoglobin (Hb) is a protein found in red blood cells, popularly known as red blood cells. It is one of the elements present in greater quantity in the blood, which gives it a red color.

The function of hemoglobin in the bloodstream is to transport oxygen throughout the body through the circulatory system. Its life span lasts around 120 days (4 months) in the body, the same as the life span of the red blood cell.

Glycated hemoglobin (HbA1c) is the product of the binding of hemoglobin to glucose, called glycation . This connection is lifelong, that is, when it occurs, it is no longer possible to separate the two parts, making them one.

Simply put, the hemoglobin synthesized by the body is pure, while glycated hemoglobin has gone through the glycation process (binding to glucose).

Finally, the amount of glucose (one of the main carbohydrates sources of energy for living organisms) in the blood is called glycemia . It is directly linked to insulin, a hormone produced by the pancreas responsible for reducing the amount of glucose in the blood.

The higher the blood glucose levels, the greater the formation of glycated hemoglobin. Therefore, a patient with uncontrolled diabetes has an elevation of HbA1c in the blood, while a patient with controlled diabetes has also controlled levels of glycated hemoglobin.

Glycated hemoglobin or glycosylated hemoglobin: what’s the difference?

In practice, the terms glycated hemoglobin and glycosylated hemoglobin are generally used interchangeably. However, it is important to point out that, from a clinical point of view, this is wrong.

Glycated hemoglobin refers to the non-enzymatic and permanent binding of sugars such as glucose to hemoglobin, which form glycated hemoglobin (HbA1).

Glycosylated hemoglobin is the name of the glycosylation process. This involves an enzymatic and unstable bond, which is basically the opposite process to what occurs in the formation of glycated hemoglobin.

Therefore, the term glycosylated hemoglobin is incorrect if it is used to refer to glycated hemoglobin, but they are generally used to indicate the same thing.

What is the glycated hemoglobin test for?

The glycated hemoglobin test may be indicated in case of suspected diabetes.

The examination of glycated hemoglobin demonstrates the percentage of glucose bound to hemoglobins (which are proteins present in red blood cells), through the analysis of collected blood.

It is used to assess the average glycemic level of the past 3 or 4 months, more or less. Therefore, it serves to monitor and assess the health of patients in routine examinations.

It also serves to confirm the diagnosis of diabetes or pre-diabetes. In addition, glycated hemoglobin is used to see adherence to treatment for diabetes. Thus, patients with the diagnosis are tested frequently to monitor how blood glucose levels are doing.

How is done?

For the examination of glycated hemoglobin it is done through a common blood collection, and in general there is no need for fasting. However, it is usually done after 2 hours of food intake, so that there is no interference due to hypertriglyceridemia (high level of fat in the blood).

The exam is safe, fast and risk free. In general, there may be only one discomfort due to the bite, but this tends to be well tolerated by most people.

The Brazilian Diabetes Society (SBD) recommends that healthy people or those with a family history of diabetes undergo the exam at least once a year. For those who have a diagnosis of diabetes, the recommendation is every 3 months or according to medical advice.

Results: what does high glycated hemoglobin mean?

When the result of glycated hemoglobin is greater than or equal to 6.5%, diabetes can be characterized, requiring a retest to confirm the diagnosis.

After confirmation, medical advice is given for the treatment of diabetes. But it is always important to take the test result to the doctor so that the result is properly interpreted.

The high result for those who have diabetes indicates the need to adjust the treatment. Reviewing food, insulin / medication doses and adopting physical exercise may be options.

What is the reference value of fasting glycated hemoglobin?

The rate considered ideal and without evidence of glycated hemoglobin (HbA1c) diabetes is established by some parameters. In general, the general diagnosis of diabetes is based on:

  • HbA1C below 5.7% = absence of diabetes;
  • HbA1C between 5.7% and 6.4% = presence of pre-diabetes;
  • HbA1C greater than or equal to 6.5% = indication of diabetes.

It is important to emphasize that the values ​​are general and do not consider individual conditions such as medical history, age, influence of other illnesses and physical characteristics of each individual.

Therefore, the interpretation and evaluation of the exam results need to be done by professionals.

Difference between glycated hemoglobin and fasting glucose

A common doubt is the difference between the fasting glucose test and the glycated hemoglobin test. The main factor that differentiates them is that the fasting blood glucose test is unable to make a “history” of the patient, indicating blood glucose levels only at the time of collection.

To illustrate more clearly, look at the following example:

If a patient with diabetes did not follow the diet prescribed by the doctor and did not use the medication correctly in her daily life, she had an increase in glycated hemoglobin.

When the doctor ordered the fasting glucose test 5 days before the test, she adhered to the diet and took the medication. When taking the results to his doctor, his glucose levels were within the reference standards.

Using the same example mentioned above, but with the glycated hemoglobin test, the results would point out the amount of hemoglobins that underwent glycation during the last few months, which would lead the doctor to identify the failure to follow the diet correctly and the medication irregularity.

Unlike the fasting blood glucose test, the glycated hemoglobin test does not only analyze the time of blood collection, but it is able to measure the concentration of hemoglobins that are linked to glucose in an average window of 90 days.

It is worth remembering that, when examining glycated hemoglobin, it is also possible to establish the mean blood glucose over the months.

The units of measurement for the fasting blood glucose test is mg / dL (milligrams per deciliter), whereas the glycated hemoglobin is in percentage. Check, below, the equivalence table between these values:

Fasting blood glucoseGlycated hemoglobin
97mg / dl5,00%
226mg / dl9,50%
269mg / dl11,00%
283mg / dl11,50%

High glycated hemoglobin: how to download?

With simple changes it is possible to lower and better control the rate of glycated hemoglobin.

Lowering high glycated hemoglobin is possible through lifestyle changes. Generally, a healthy diet, regular exercise, the use of medication for the treatment, among other habits, is recommended.

Better understand how to adhere to better control:

Healthy eating

Adjusting the routine and adhering to healthy eating is a very important point in regulating glycated hemoglobin. Often, this alone can be enough to improve exam values:

  • Eat more fiber: a meal with fiber slows down the entry of glucose into the bloodstream – that is, it is released slowly, which avoids spikes in blood glucose right after the meal. This can even help to reduce hypoglycemia;
  • Combining protein and / or fiber with meals: foods with a high carbohydrate index (like some fruits) can be balanced with the addition of a source of protein or fiber;
  • Avoid several carbohydrates in a single meal: choose a type (such as white rice, white breads or pasta) and combine it with lean meats or vegetable proteins and fibers;
  • Making exchanges: there are several options called diet, which are especially suitable for people with diabetes. This reduces carbohydrate intake, facilitating glycemic control.

Remember to always consult nutritionists and endocrinology specialists to plan your diet.

Attention to weight

Controlling weight is one of the ways to lower the rate of glycated hemoglobin, as there is a direct relationship with type 2 diabetes. This is because the body is more predisposed to insulin resistance.

With changes in diet, medical follow-up and regular physical activity, it is easier to lose excess weight and stabilize blood glucose.

Physical activities

With the practice of physical activities, the muscles remove glucose from the bloodstream, “expending” and decreasing the rate in the long run. In addition, regular exercise helps to decrease body weight.

For there to be benefits with practice, 150 minutes of weekly physical activity is recommended, that is, 30 minutes 5 times a week.


The use of medication prescribed by a doctor, when necessary, is important and should be done responsibly.

Taking medication at the right time, re-evaluating dosages frequently and keeping your appointment up to date makes all the difference.

There are different medications that can be used, depending on the diagnosis. Among them, insulin (type 1 diabetes or insulin dependent) or oral medications (usually, type 2 diabetes or pre-diabetes).

Health care is important throughout life. For this, medical monitoring is necessary to clarify doubts and assist in disease prevention.

Check out the Healthy Minute for more information on health care and tips on how to maintain a healthier life.